Command terms

Every structured question part begins with a command term: a verb such as state, explain or determine that says what kind of answer is wanted. The IB defines each term precisely, and markschemes are written to those definitions. An answer that is correct physics but of the wrong kind, a bare value where reasons were asked for or a paragraph where a single word would do, can lose most of its marks.

All the command terms at a glance

The physics course has its own short glossary of seventeen command terms, grouped by the assessment objective each one tests: knowledge (AO1), application (AO2) and analysis and evaluation (AO3). Calculate, determine, explain, outline, show that and state together make up about two thirds of all structured question parts on past papers.

Other instruction words are allowed, and several appear regularly on papers. Their meanings follow the general IB glossary. "Show that" is by far the most common; the rest are occasional.

"Hence" is not a command term on its own, but it changes the meaning of the one it accompanies. "Hence calculate" means "use the previous answer to calculate"; "hence or otherwise" allows any method.

Naming and recalling

State

Give a specific name, value or other brief answer. No explanation or working is needed. A one-mark state is a word, a phrase or a number with its unit; a two-mark state is usually two items, or "state and explain".

Define (also seen on papers)

Give the precise meaning of a term or quantity, worded so that it would fit any situation. A definition of a quantity usually names a ratio or a rate, and a definition by equation must say what each symbol means. Recent papers often use "State what is meant by …" instead.

Identify

Pick out one answer from several possibilities: a point on a graph, a variable, a particle, a region of a diagram. A bare answer is enough.

Calculations and values

Calculate

Obtain a numerical answer, showing the relevant working. A typical two-mark calculate gives one mark for the substitution or method and one for the answer. A correct answer with no working usually still scores if the markscheme allows a bald correct answer, but any slip then loses everything.

Determine

Obtain the only possible answer. Determine is often used for multi-step calculations and for values that must be read from a graph or a diagram ("Determine, using the graph, …", "Determine, taking measurements from the diagram, …"). Show where each value came from.

Estimate

Obtain an approximate value. Estimate is used when data must be read roughly from a graph, when an order of magnitude is enough, or when some quantity has to be assumed. State any value you assume, and give the answer to one or two significant figures. Markschemes accept a range.

Show

Give the steps in a calculation or derivation, without a final value being given in the question. Show is rare on its own; it is marked like a derivation.

Show that

Reach a result that the question gives. Because the answer is known, the marks are entirely for the method. For a numerical result, show the full substitution and give your answer to at least one more significant figure than the "about" value in the question. For an algebraic result, start from a stated principle and show each step.

Deduce

Reach a conclusion from the information given. A deduce answer has two parts: the reasoning or calculation, and the conclusion it leads to. The conclusion mark usually depends on the reasoning mark, so a bare "yes" or "no" scores nothing.

Written accounts

Outline

Give a brief account or summary, usually one or two linked points. An outline does not need the full chain of reasoning that an explanation needs.

Describe

Give a detailed account of what happens, or of what to do in an experiment, without giving reasons. Descriptions of method should be specific enough to follow: name the instruments, the quantities measured and how.

Explain

Give a detailed account including the reasons or causes. Each step in the chain of cause and effect is usually worth one mark, so a three-mark explain needs three linked statements, finishing with the quantity the question asked about.

Compare, and compare and contrast (also seen on papers)

Compare asks for similarities between two or more items, and compare and contrast for similarities and differences. Every point must refer to both items, so a good answer uses "both" or "whereas" in each sentence.

Distinguish (also seen on papers)

Make clear the differences between two or more concepts or items. A two-mark distinguish needs a point about each, linked by a contrast.

Judging and evaluating

Analyse

Break down a situation, a set of data or an argument to bring out its essential elements or structure. In physics this often means identifying the trend in data, the factors that affect a quantity, or the stages of a process.

Discuss

Offer a considered and balanced review that includes a range of arguments, factors or hypotheses. Each valid point usually earns one mark, so a two-mark discuss needs two distinct points, and a conclusion where one is called for.

Evaluate (also seen on papers)

Make an appraisal by weighing up strengths and limitations, then reach a judgement. In physics this is often applied to a method, a model or a source of energy.

Comment (also seen on papers)

Give a judgement based on a given statement or the result of a calculation. A comment on an experimental result usually compares it with an accepted value, taking the uncertainty into account.

Predict

Give an expected result, usually with a reason. "Predict, with reference to …" requires the reason to use the named idea. A bald correct prediction may earn one mark when the command is only predict.

Suggest

Propose a solution, hypothesis or other possible answer. Suggest is used where several answers are acceptable, often for an improvement to an experiment or an explanation of an unexpected result. A reason linked to the situation is usually needed.

Justify (also seen on papers)

Give valid reasons or evidence that support an answer or a conclusion. A justification refers to data, a principle or a calculation, not to opinion.

Graphs and diagrams

Draw

Represent something by an accurate, labelled diagram or graph, using a ruler for straight lines. Diagrams should be to scale where possible; graphs should have plotted points and a line or smooth curve. Marks go for direction, relative size, the correct point of application and labels.

Sketch

Represent the general shape of a graph or diagram, with its relevant features labelled. A sketch need not be to scale, but its axes must be labelled with the quantities, and its features (intercepts, gradients, maxima, asymptotes, relative heights) must be correct.

Plot (also seen on papers)

Mark the position of points on a graph accurately, usually from a data table. Each point should be within half a small square of its true position.

Label (also seen on papers)

Add labels or names to a diagram, such as nodes and antinodes on a standing wave, components in a circuit, or regions on a Hertzsprung–Russell diagram.

Annotate

Add brief notes to a diagram or graph, explaining what a feature shows rather than only naming it.

Construct (also seen on papers)

Display information in a diagrammatic or logical form, such as an energy-level diagram, a free-body diagram or a table of results.

Using command terms in practice

Underline the command term in every part before answering, and check the mark allocation. Then decide what the answer must contain:

• A value only (state, identify)?

• A value with working (calculate, determine, estimate)?

• Every step of a given result (show, show that)?

• A chain of reasons (explain, justify, predict with a reason)?

• Several points weighed against each other (discuss, evaluate, compare)?

• A drawing with specific features (draw, sketch, label, annotate)?

Self-check

• To do:

  I can say what each command term asks for and how much it is usually worth.

• To do:

  I can tell the difference between state, outline, describe and explain, and write each kind of answer.

• To do:

  I can set out calculate, determine and estimate answers with working, and show that answers with every step.

• To do:

  I can write a deduce answer with both the reasoning and the conclusion.

• To do:

  I can write compare, distinguish and discuss answers with distinct points that refer to both items.

• To do:

  I can give a comment or a justification based on data and uncertainties.

• To do:

  I can tell what a sketch needs from what a drawing needs, and include every relevant feature.